1. Field of the Invention
The invention relates to image forming apparatuses such as electrophotographic copying machines. More particularly, the invention is directed to an image forming apparatus such as an electrophotographic copying machine that employs an endless belt-like, thin plate-like light-transmitting photosensitive body and discharges the photosensitive body and/or forms screen patterns for photographic reproduction by irradiating a beam from the back surface of the photosensitive body.
2. Related Art
The above-described image forming apparatus performs the operation of discharging the photosensitive body and/or erasing unnecessary images and/or forming screen patterns for improving photographic reproducibility (or tone) by irradiating a beam from the back surface of the photosensitive body while utilizing the light-transmitting property of the material of which the photosensitive body is made.
FIG. 15 shows a schematic construction of the above-described image forming apparatus. In FIG. 15, reference numeral 1 designates an endless belt-like photosensitive body installed onto a drive roll 2 and driven rolls 3, 4. Arranged on the front surface of this photosensitive body 1 are, from the upstream side in the direction of moving the photosensitive body 1, a charging unit 5 for charging the photosensitive body 1; an image exposing irradiating section 6 for forming a latent image by irradiating an image exposing beam 6a onto the front surface of the photosensitive body 1; a developing unit 7 for developing a toner image from the latent image; a transfer unit 9 for transferring the toner image onto a sheet fed by a sheet feeding means 8; a separating unit 10 for separating the sheet having the toner image transferred thereon from the photosensitive body 1, and a cleaning unit 11. Reference numeral 11a designates a sheet forwarding means for forwarding the sheet separated by the separating unit 10 to a fixing unit 12. Reference numerals 28a, 28b, 28c designate other rolls or bars.
The photosensitive body 1 is made of a light-transmitting photosensitive material. On the back surface of the photosensitive body 1 are two units: a discharging unit 13 for discharging the photosensitive body 1 by irradiating a beam onto the back surface of the photosensitive body as well as the upstream sides of the charging unit 5 and the transfer unit 9; and an unnecessary image erasing unit and/or screen pattern forming unit 14 positioned on the downstream side of the image exposing irradiating section 6.
When the back surface of the photosensitive body 1 of the thus constructed image forming apparatus becomes dirty, the beam from the discharging unit 13 and the unnecessary image erasing unit and/or screen pattern forming unit 14 irradiated from the back surface of the photosensitive body 1 is blocked by the dirt, thereby decreasing the amount of light reaching a charge generating layer stacked on the front surface of the base material of the photosensitive body 1 and causing various inconveniences.
The back surface of the photosensitive body 1 must therefore be cleaned by some means in the above-described image forming apparatus such as an electrophotographic copying machine.
Conventional cleaning members are disclosed in Unexamined Japanese Patent Application (OPI) Nos. Sho. 60-144780, Sho. 60-144781 and Unexamined Japanese Utility Model Applications Nos. Sho. 60-98857 and Sho. 60-98858.
The following problems have been encountered by these conventional cleaning members. The potential generated on the back surface of the photosensitive body is increased by triboelectricity or the like. This attracts the developer, paper powder, dust or the like more strongly to the back surface of the photosensitive body, and therefore may sometimes make mechanical cleaning insufficient. On the other hand, only the discharging of the back surface of the photosensitive body is not adequate to prevent adhesion of the developer, paper powder, dust or the like to the back surface of the photosensitive body.